


"Trading Spaces!" or "In the Name of SCIENCE!"

by equilateral_asshat



Category: Gravity Falls
Genre: Bodyswap, Electron Carpet, F/M, Wendy is only there for a brief moment but I thought she deserved a tag, pinecest - Freeform, pinescest - Freeform
Language: English
Status: Completed
Published: 2018-12-15
Updated: 2018-12-15
Packaged: 2019-09-18 11:28:31
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,966
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16994151
Author URL: https://archiveofourown.org/users/equilateral_asshat/pseuds/equilateral_asshat





	"Trading Spaces!" or "In the Name of SCIENCE!"

In a quiet room in the Mystery Shack, a sound emerged. Feet scuffling over a shag carpet, followed by the short, sizzling SNAP of static discharge, and a pair of groans.

“Whoa, this is… different.” Dipper looked down at his hands. Well, they weren’t really his hands; they were Mabel’s. She seemed to be having the same response off to the side, inspecting the fingernails on her brother’s hands. “I mean, this isn’t the first time I’ve piloted this thing-”

“Hey! My body is not a ‘thing’ young lady,” Mabel mock-chastised her brother. He immediately blew a raspberry at his own face. He’d likely never get used to that.

“You know what I mean, Mabes! The last time we swapped bodies we weren’t so different. Now I’ve got, well…” he explained, gesturing to Mabel’s breasts. Or were they his breasts while he was in her body? This sort of thing was not easy for him to process logically. She smirked (or, rather, his face smirked) at him, followed by a an over-exaggerated wink.

“Yeah well you’ve only got'em for 24 hours, sister. So I expect them back in the same shape I left them in!” He rolled his (her?) eyes at that. Then, with a blink, he felt himself blushing.

“So, wait… what happens when we have to like, shower and take baths and stuff later?” His sister was lost in the process of giving his arms a flex and squeeze, as if trying to see if they were really limp noodles or not. He knew they weren’t, anymore; he just wasn’t bulky. He’d developed a lot of sinewy, wiry muscles that had deceptive strength to them.

“I'unno, I figure we’re both eighteen, what’s it matter if we see naked bodies? I mean shoot, I’ve seen your internet history!” He groaned, burying his now feminine face in his-but-his-sister’s hands. He then marveled at the smoothness of the skin against those hands before his mind came back to the topic at hand.

“You know what I mean, Mabel! Seeing other people naked is one thing, seeing each other nude is a different thing entirely!” His shoulders shrugged at him, while the expression on his face was very much his sister’s.

“Bro-sis, we used to take baths together all the time.” He tugged at the locks on top of the head his psyche currently inhabited, and wow that was some really soft hair up there. His sister took really, really good care of herself. Maybe when they swapped back he could get some beauty tips from her. He’d just have to word that differently.

“We were five years old!” He felt his current set of eyes blink. “Hey, uh, didn’t I still have my own voice last time we did this?”

He watched Mabel blink in his body. She cleared her (his) throat and then quickly sang out, “Do, Ray, Me, Fa, So, La, Ti, Do!” She laughed; to Dipper, hearing words and laughter come out in his own voice, but with her inflection, was distracting. “Hahaha, that’s neat.”

Dipper just sighed, shoulders slumping. “Why did I even agree to this again?”

“For SCIENCE!” he heard his own voice proclaim over-enthusiastically. “Also I think one of us bet the other we couldn’t stand being in the other’s body for an entire day? I think I'ma win though, sis-bro.”

With a shrug of the shoulders, he had to resign that yeah, the scientific aspects of being in a different body for an entire day were appealing. So was the wager that he and Mabel had placed on this endurance challenge; the winning twin got to decide what movie marathon theme they were doing next. Mabel wanted to do her sappy teenage romance movies from the eighties, and Dipper would rather do monster movies. Whoever caved first gave up their right to choose this week.

“Whatever, Mabel. Let’s just get this day over with.”

“Hey, YOU’RE Mabel now. I’m Dipper Pines, sweaty eighteen year old nerd extraordinaire!” Mabel proclaimed, motioning with jazz-hands. Dipper felt his now feminine lips curl into a sly smile. “What uh, what’s so funny about that?”

“Well, if I’M Mabel now, that makes me the alpha twin!” He fist pumped, very much in her style. Maybe this body swap would have its advantages!

———  
———

Dipper had decided that this did, in fact, NOT have advantages. Normally he adored his standard, somewhat-boring cereal. But today for whatever reason it tasted like sawdust soaked in water and glue. He swirled around with a spoon, looking slightly dejected. Mabel was having her own problems with her bowl of brightly colored fruity flavored, sugar-and-marshmallow laden cereal.

“Ugh, something must be wrong with me because this stuff tastes too sweet,” she grumbled, shoving the bowl away. Dipper stared at the bowl she’d just shoved way, and then back to the one setting in front of himself.

“Okay, call me crazy, but let’s trade,” he said, quickly pushing the bowl of bran towards his own body while yanking the rainbow colored nightmare in a bowl towards himself. Each dipped a spoon into their new bowls, looked at the other hopefully, and took a bite.

“Wh… why do I like this stuff?! Normally this cereal tastes like-” Mabel started, but Dipper cut his twin sister off.

“Let me guess, sawdust soaked in glue?” He watched his sister nod his own head at him furiously as she shoveled more into his mouth. “Yeah, normally this stuff just tastes like candy soaked in syrup to me and I could even stand to sugar it a little, right now.”

“Whoa… wait, so if I’m in your body I’m gonna like the food you normally like to eat?” He nodded. “Dang, I never thought I’d be glad to hear my food was gonna be boring.”

“Hey, this is no easy thing for me either. My brain says I shouldn’t be eating this stuff but _your tongue_ insists I keep shoveling it in.” She shrugged at him, and they sat in relative silence as they inhaled the rest of their breakfasts.

Thankfully, they’d picked a day of the week when the Mystery Shack was closed. Their grunkles were watching the tourist trap while Soos and Melody honeymooned, and had taken off to go fishing earlier that day. The twins had all day to themselves, practically, to figure out this ordeal with the swapped bodies.

Mabel seemed to be having a swell time, from Dipper’s perspective, but secretly she felt just as awkward as he did. Her face being fuzzy to the touch, her taste buds being so boring, and the way clothes fit on this body, ugh, man. She was having trouble keeping his shirt straightened out because she wasn’t used to his typical, slouchy posture from all the reading he did. _If his back always hurts this much why doesn’t he say something?! Yikes._

Worst of all, so far, was dealing with the one thing that all teenage boys dealt with throughout their lives; random boners. She didn’t even have to be having naughty thoughts of any sort, it seemed. Just, boom, hello, poppin’ up to say hi! She figured, after the third one of the day, that either Dipper knew some strange secret to keeping it from doing that or secretly felt pride. Because hoo-boy, if this were any other guy’s body she might be admiring that thing. Was that weird of her? To have slightly naughty thoughts about her own brother’s dongle while she inhabited his meatsuit? She’d just blame it on the hormones.

She was busying herself with sweeping the Shack’s gift shop when she heard the back door swing open and heavy footsteps clomp through the building towards her. “Hey, Dip, Mabel, either of you guys h-oh hey Dipper!” Mabel spun around to see Wendy standing there, white tank top, ripped up jeans, green flannel shirt tied around her waist. The older girl ran a hand through her hair and settled Dipper’s old hat back on her head. They were still doing that we-totally-aren’t-a-couple-hat-trade thing that Mabel maintained was code for 'Once you’re legal we’re gonna bang.’

“Oh, uh, hey there Blerb-dawg!” _Oh, dammit, Mabel! You’re in Dipper’s body, don’t say that stuff!_ “I mean, Wendy. What brings you in today?” Ah, she saved it. Wendy perked a brow at the awkward teenager standing in front of her and gave the masculine chest a friendly jab.

“You have been spending WAY too much time with your sister if you’re gonna start callin’ me 'Blerbdawg’, dude. I think I left my phone here last night,” she explained, leaning over the front of counter and digging in an open drawer. Mabel watched with interest. Maybe too much interest. She caught herself staring at the way Wendy’s curvy rump wiggled this way and that as she dug around, and the grunting sounds she made while she busied herself, oh man! Wait, why was this hot? She didn’t like girls! Well, maybe a little bit but now she was certain that Dipper’s body was-oh, yep, there it is. Hello boner. She quickly managed to shuffle her pants around until it wasn’t noticeable, just a split second before Wendy stood back up, phone in hand. “Aha! Got it. Tell your sis I said hey, alright? Seeya Monday!”

Mabel stood there, sweaty and awkward. Was this what it always felt like to be Dipper? Man this was awful. And awful was the opposite of that freckly redhead’s luscious looking booty. Wait, NO, there went her brain again, letting the body do the talking. Ugh, she was gonna have to talk to Dippin’ Dot about this if it kept up. This didn’t feel normal, at least not “Mabel” normal.

———  
———

Truth be told, Dipper wasn’t faring much better on his end. He had taken it upon himself to channel surf for the first half of the day, and found himself flipping channels every time a cute guy showed up on the screen. If he left the channel linger too long, his stomach started to fill up with butterflies and that spot between his legs he was trying to ignore, and failing to do so, would tingle. It was strange enough to have to continuously touch his sister’s breasts whenever her bra slipped.

He’d never been into guys, what was causing it now? Unless… well, of course it made sense. Mabel’s body used Mabel’s hormones, so it stood to reason that seeing what her body might perceive as a desirable partner would cause these reactions. But he didn’t want to deal with those reactions. He’d already made it a point to avoid Wendy when he saw her pull up earlier; female body or not that girl was always going to be hot. No sense in getting his sister’s body into women, too. Wait, did it work like that? Would traces of his psyche linger? He’d have to take notes before and after they swapped into their own bodies later. He was jotting notes down in a notebook when his sister tromped in, in his own body, and flopped heavily against the arm of the yellow chair he was occupying.

“Hey, 'sup with you? You’re look kinda flustered there, brother,” he teased, trying to give her that telltale teasing eyebrow wiggle thing. The look she shot him suggested he wasn’t any good at that. “But no, really Mabel, what’s up?”

“So, uh… weird question here, Dip. How do you manage to make certain… reactions? I guess you could call it. Yeah, how do you make certain reactions calm down and go away?” Dipper clicked his pen a few times, then straightened his sister’s posture. Her back couldn’t hunch like he normally did, oof.

“What kind of reactions? You didn’t try to eat anything I’m allergic to, did you?” His own head shook back at him hastily. “What do you mean th-OH MY GOD. Hahaha, Mabel Pines had her first erection!” he teased, doing the eyebrow waggle again. This time it must have worked because she glared at her own tactic being used against her. And with her own body, no less!

“About half a dozen, actually. Seriously, is this why guys are always thinkin’ about bonin’?”

“Okay first of all, that’s just a myth. I don’t think about it as much as I usually could. And the way this body tingles when it sees cute guys on the TV screen alone is just as bad!” Mabel huffed, and he watched her cross his arms over his chest defensively. “I’m sorry, sorry. Just weird, yanno? Anyhow, you have two options to make those stop.”

“Go oooonnnn…” she inquired, batting his eyelashes at him. Wow, her expressions did not work with his face.

“Option one; you’ve seen my internet history.” She nodded, then he watched the color drain from his own face, before it flushed back twice as fast. No wonder people laughed when that happened, it was actually amusing to see!

“Ew, god, no! I’m not touchin’ it like that! It’s bad enough I have to keep adjusting it, it’s worse than boobs!” He felt blood rise on her face this time. She’d been readjusting it every time? She’d touched it?! Man, this made her body do even weirder flutters. He forced his mind to focus.

“Option two; cold. Cold causes shrinkage, shrinkage reduces the swelling. They recommend cold showers for a reason, Mabel.” The entire time he was explaining this, he scribbled down notes, even in the margins of his other notes. She leaned over to try and peak at what he was writing, but somehow his usually legible handwriting looked abysmal.

“Whoa, what’s with the jittery word-scribbles, Dip? You okay?” He nodded, running some fingers through a chunk of her hair.

“Yeah, I’m fine, but I’m not used to writing with your hands. This whole situation is a little overwhelming. I guess we usually take a lot of things we learn to do on autopilot for granted…” He sighed heavily, leaning back with a groan. “I am feeling kind of woozy, though. I hope I haven’t gotten you sick or anything when we switch back.”

“Woozy? When’s the last time you had anything sugary? I usually graze on glucose all day long,” she explained, and she watched her brother light up behind her own eyes. “You sit tight, I’ll bring you a glass of Mabel Juice.”

“Whoa, wait, I don-oh, yeah. I guess in your body I’ll handle it just fine, heh.” He smiled an apology her way, and she just snapped fingerguns at him. When she walked away towards the kitchen, he got his pen back out and started to write even more notes.

_-Little things become quickly noticeable as a person gets used to the new body they’re in; most noticeable to me has been watching Mabel walk around like herself, but in my body. It’s odd to see me prance about so gaily. I’ve also noticed that while we have the other person’s voice, our usual inflections and tone carry over, making it easy to tell something is off. Uses of the rug for spying or infiltration seem small unless one would need a specific bio-signature or DNA to get into a high security area. And, despite what I saw our first summer here, I highly doubt anything like that is-_

“One mega-shot of Mabel juice, fresh for you!” A glass full of ice, green juice, what appeared to be glittery sugar and… was that an army man? Appeared in his vision. Normally the syrupy sweet smell would turn his stomach, but to his sister’s body it smelled of ambrosia. He snatched the glass and chugged the delightful elixir. “Nice to see somebody finally appreciating my mixology talents!”

“Well, normally I can’t stand this stuff because it’s too sweet, for my tongue. Your tongue certainly likes it. This is the breakfast situation all over again, why didn’t I realize I’d need sugar to keep running.” He slammed back the rest of the glass, spitting the little plastic rifleman back into the glass with a satisfied sigh. “Thank you.”

“No problemo. But, you’re gonna be feeling energetic pretty soon, that was a super-concentrated glass. What’s say we take these bodies for a proper field test and go for a quick run on the forest trail?” Mabel suggested, and he felt a smile spreading over his sister’s features. “We just, uh… gotta change into proper running… outfits…”

Each twin blushed, looking down at their sibling’s body. Yeah, they’d been inside of them all day and outside of random arousal, nothing too uncomfortable had happened to either. They both silently, simultaneously decided that if their sibling was going to be freaked out by seeing them naked, oh well. They went up the stairs, into the attic, to change.

They decided together it would be best if the other person chose the outfit for their own body, and once they had everything sorted out Dipper just stared at the wall. “So, um, you want the bathroom to change or..?”

“Well, to be real honest, you haven’t got anything I’ve never seen before, Dipperoo. What’s the hurry to get some alone time with my naked bod? You thinkin’ of gettin’ weird?” Mabel teased. He groaned, tossing a pillow at his own face as it donned one of his sister’s smirks.

“Fine then, let’s strip!” he challenged her, hastily pulling the clothing off of her body. She readily accepted the challenge, shucking his outfit in a hurry as well. Once they were both in the buff, they paused to regard one another.

Dipper noticed, staring at his own body from this perspective, that maybe he was better looking than he gave himself credit for. His limbs weren’t gangly so much as wiry, and he had filled out nicely over the years. Plus when his gaze wandered below his waistline, whoa. It certainly looked bigger from this angle. Why did that make those butterflies come back? Was his sister’s body getting aroused by his?! Was _he_?! He quickly buried that notion in the back of his mind, unaware that Mabel was going through a similar quandary.

Sure, she was hot! Mabel had always known she was hot. But seeing herself naked, with a guy’s hormones surging through the body she was in? She found a whole new appreciation for just _how_ hot she was. Her breasts, while not the biggest were perky. The curve of her butt as almost like a perfect little hemisphere, and her legs oooohhhh maaaannn… uh oh. She quickly forced herself to look away and think unsexy thoughts, lest Dipper notice his sister getting a boner over herself. Oh god, was it just her having that response, or was his body also into it?! UGH it was so confusing.

They both hurried into their respective outfits, tugged on running shoes, and set out for a jog to distract themselves. All in all, it was nice having a chance to not focus on this weird experiment. They just jogged and chit-chatted about life and whatnot. Dipper was starting to finally feel relaxed in his sister’s skin, and Mabel seemed to be forgetting the awkward experience of popping a half-chub over her own body. They ran for a good while, then slowed to a walk for the trip back, each panting and sweaty.

When they got back to the shack, Dipper grabbed a bottle of water from a cooler on the porch and upended it over his sister’s body. Yeah, running felt great, especially with all the energy that concoction she gave him earlier had provided! But he felt like he was burning up. He hummed happily as the cool water doused the lithe frame he was inhabiting.

Just behind him, Mabel was forcing herself to not watch that spectacle. Skin tight shorts, sweat beading on her body where fabric didn’t cover it and now her brother was pouring water all over it so lewdly! “I, uh, I think I’m gonna go take a shower. No offense, bro, but you smell even worse after a run than you do after lounging around all day like a nerd,” she hurriedly offered, trying to walk into the shack nonchalantly. Dipper just hummed in acknowledgement as his body tromped past.

He caught himself staring at his broad shoulders and wow, did he even have a cute butt? Man girl bodies were weird if they liked this stuff. Ah well, he’d take notes about this later. He wrung out his sister’s long locks, then went and sat back in that old yellow chair as he waited for the shower to clear up. He had to admit Mabel didn’t smell like sunshine and roses after a long run either.

His sister, in the meantime, started with a nice hot shower. Man, her bro-bro’s body could tolerate a lot of heat. It felt good to let the near-scalding water rinse off the smell of sweat and dirt. She felt muscles relaxing, aches and pains soothed away. The easing tension gave way to wandering shower thoughts. And before long those thoughts fell once again on things like Wendy’s butt and her own body getting doused with cold water. The way it plastered that sheer shirt down to the front of her body, highlighting the curve of her own breasts and those tense nipples, that had been a hell of a sight! No wonder guys stared. And-uh oh. There it was again. The _Boner_.

“Can we not do this, body? I don’t…. I don’t wanna have to touch Dipper’s bits like that.” The only answer she got from the growing arousal between her brother’s legs was a throb in tempo with the beat of the heart in his chest. She groaned. It didn’t seem to be going anywhere this time. Only one solution. With great resignation, she circled the base of his manhood with a loose grip and gave an experimental pump. Well, that wasn’t so bad, she guessed. She tightened the grip and gave another. Oh, oh man so it wasn’t exactly like when she did her lady-time, but she could definitely see why teenage boys did this stuff now. With each passing second of her experimental motions, the pace of the hand around that member quickened. She felt a coil tightening in her brother’s gut, closer, _closer…_

A loud rap on the door made her jump, her focus on the task at hand gone. “Hey, Mabes? You about done in there? I’m feeling a bit ripe myself and I don’t wanna stink your clothes up as bad as I tend to my own,” called her own voice. She groaned, the moment lost, that sensation of mounting pressure gone. She reached out, shut the hot water off and let cold pour over her brother’s body. The shock caused an immediate response, his member quickly shrinking down. Welp, he was right about that at least!

“Yeah, lemme get a towel on and it’s all yours,” she replied, wrapping the towel around the torso she currently called home. Why did it seem so short, it never-oh, right. Dipper’s bod. He was a tiny bit taller than her now. She lowered the towel around his waist and cinched it in place before opening the door. “All yours! Don’t scorch my skin though, sis. I don’t like my showers as hot as yours, apparently.”

“Duly noted,” Dipper replied, and for a second Mabel could have sworn he seemed to be looking his body over. Did… did he know what she was just doing? How could he know? Was she flushed? What tells did the male body have for 'hey I just tried to crank one out’? Oh man. But after a brief moment of awkward eye contact, each twin swapped places on their sides of the door and it closed in a hurry.

 _Good god, even hotter glistening wet. Why does my own body turn Mabel’s body on so much?_ Dipper ran these recent events over and over again in his mind’s eye, trying to make sense of it all. Was it just her hormones? Was there maybe a tiny bit of narcissism in this attraction to himself? He shook these thoughts away as he turned on a stream of water, at a normally cooler temperature than he would if he was in his own body. Mabel’s more delicate skin seemed to relish the cooler-but-still-warm temperature, causing a throaty sigh to escape her lips as he felt her body start to relax.

Without much thought, Dipper fished out her body wash and a washcloth, lathering up a nice fruity foam that he quickly scrubbed into her various nooks and crannies. He silently wondered to himself if Mabel had such an easy time washing his body off like this, or if having to touch his private areas had made her shy. She did seem kind of awkward standing there. Had she…? Nah, she said she wasn’t going to do that. But what if she had? What if she’d fooled around, grabbed a hold of his dick and tried to rub one out?

A feminine gasp escaped his sister’s lips and he realized that her fingers had wandered between her legs, entirely of their own accord, and had rubbed over his sister’s most sensitive spot down there. He’d just started shlicking to the thought of his sister jacking off in his own body. What’s more, he wasn’t stopping just yet. Okay, now.

…now. Right now. With determination, he tugged the hand away from the electrified spot there and decided to see if cold water worked on women as well as men. The answer, as icy water pelted his sister’s creamy skin, seemed to be yes. It at least shocked the horny straight out of her body in the meantime. He quickly shut the water off, coiled up in a towel, and then remembered to do that weird towel-hat thing she had showed him once to soak up excess water that was in her hair. “Okay, time to go get dressed. Hopefully Mabes already got her half of that finished so I don’t have to see me naked anymore.”

 _There are sentences you use everyday, and then there’s stuff like that,_ he thought, head shaking. He padded barefoot from the bathroom to the stairs, ascending quietly. Mabel’s smaller frame and lighter mass made sneaking easy. No wonder she had such an easy time spooking him constantly! Maybe he could convince her to wear a bell of some sort once this was all over? While he tried to think of a way to do just that, he opened the door to their shared room in the attic and almost suffered a heart attack.

“DIPPER OH GOD, IT-IT’S NOT WHAT IT LOOKS LIKE!” Mabel panicked, grabbing a pillow and shoving it over his body’s lap roughly, his face red. Too red for sunburn. Dipper couldn’t believe it; Mabel was up here spanking it the whole time? A flurry of emotions rose under the surface of his consciousness and he wasn’t sure how many were his own and how much of it was her body causing the response.

“Are you sure about that? Because it looks like you’re sitting on your bed with my dick in y-MY hand. And it looks like you were going for the gold there, too!” The tirade came out as half yell, half teasing and he wasn’t sure if that was even possible. He glared at his own eyes, which so clearly held his sister behind them. One good thing about this swap; they had the same eyes. He didn’t feel so strange about that. And-wait, were there tears building up in his eyes? The ones on his own face. Uh oh. “H-hey, Mabes, don’t cry I just… it’s kind of a shock to walk in on your sister jacking off in your own body so enthusiastically?”

She nodded at him as he plopped down on the bed next to her. “I just… it wouldn’t go away! I almost took care of it in the shower but then you knocked so I had to use the cold water trick but once I was warm again it just, BOING!” She moved the pillow for emphasis and yep, sure enough there was Dipper’s erection. He was familiar with it. Shit, he grew up with it. But seeing it from this new angle was interesting from both scientific standpoints and hormonal ones. He felt butterflies swirl around in his sister’s insides again. That feeling not too unlike an itch was back between her legs.

“Well, I uh… if it helps you feel better I had to stop myself from buffin’ your muffin while I was in the shower?” He felt eyes bore into him, and when he met them he wasn’t sure which emotion they held; disgust? Curiosity? Embarrassment? “I didn’t even realize it was happening until the tips of my-uh, your fingers brushed over y-your cl…. Your cl-cl-”

“Clitoris, Dipper. It’s a medical term, why’s it so hard to say?” He groaned, then gave the tip of his dick a gentle flick which made Mabel yipe.

“Why can’t you use the word erection?” His face turned red. “Exactly. It’s kind of weird talking about sex stuff with you. I mean, even though we’re twins, and we’re best friends. You gave me far too many details about one of your last dates-”

“Hey I was excited and he was super duper nice! How was I supposed to know he expected me to move in with his mother after our fourth date?!” She shuddered. “Man that lady was creepy. I think she might have been a witch.”

“You never told me about th-no, not right now. That’s not what this conversation is about.” He sighed and pinched the bridge of his sister’s nose in thought. “So, we’re both getting horny and neither of us knows how to handle it.”

“Hey, hey whoa, you better not be suggesting we bang because-”

“What?! No! I might be talking to you about masturbation but I’m not gonna suggest we do THAT Mabel, sheesh. Give me SOME credit.” He gave his own shoulder a playful little punch. She grunted and rolled her eyes. “I was… just gonna say maybe we both, I dunno, help the other figure it out? The masturbation stuff, I mean.”

She glared at him. Her own face was there, but his eyes were on it. Sincere and holding that look she knew all too well. “For scientific purposes, ya mean?” He cleared her throat.

“Yes, strictly for science. I mean, we’ll be the first people on the planet to truly experience the opposite gender’s orgasm! Isn’t that amazing?!” Okay, she did have to admit that was pretty cool. “So, uh, how do… how do we start?”

“I can just pick up where I left off, I mean…?” He nodded.

“Yeah, yeah, that uh… That sounds good.” He watched expectantly, eyes glued to his own crotch as he shucked the towel he’d wrapped around his sister’s body. The moment his legs parted and his fingers hovered over her southern reaches, Mabel couldn’t help it, immediately grabbing that dick in her-well, HIS-hand, and pumping away slowly. Dipper’s eyes seemed to sparkle on her face as he watched.

While the scientific half of his mind was racing with the breadth of knowledge this could hold for the future, the other half was marveling at how strangely sexy it was to see himself jack off. It made little shivers run up Mabel’s spine, his brain feeling electric as fingertips danced over his borrowed ladyparts. It didn’t seem to matter where he touched, everywhere down there was yearning for a caress or a rub. The only spot that seemed to matter more was that button, and every time he hit it, his current vessel shuddered. How did nipples get this perky? How sensitive were they? He gave one a soft pinch and gasped, legs clamping shut immediately. Oh MAN. _That_ sensitive, huh?

Mabel, however, didn’t seem to be having as easy a time doing what she was doing, her grip somewhat clumsy. Eventually, Dipper reached out towards his own lap, the hand retracting a moment later. “Um, y… you’re doing it wrong.”

“What?” She glanced over at her brother, then back down to the outstretched hand that was reaching for his dick.

“I said you’re doing it wrong. You gotta, just… here, may I?” Slender fingers wrapped around veined, turgid flesh, and he felt his sister’s heart quicken. And his own, through his grip around his own member. How did something that should be so familiar feel so exotic and new? His grip slid up and down the length of his dick, twisting and squeezing in the spots only he seemed to know. “Dicks are kind of weird, truth be told. We think they’re all the same but they each respond differently to little things…”

Mabel just nodded, hands clenching into her sheets. The spectacle of her own feminine hand wrapped around her brother’s cock, and being the one to feel it there was starting to be too much. Why did doing this sort of thing with her bro-bro excite her this much? Would he let her do this herself when they switched back? Why did she want that to happen?! “D-Dipper?”

When their eyes met, no other words came. Instantly they gravitated towards each other, lips finding lips, the kiss deepening swiftly. When the time came to remember the event later on, neither would remember whose tongue made the first exploratory slip into the others mouth. They would only remember how strange it was to taste themselves, and how right it felt to feel their lips together no matter which body they were in. The hand on the member pumped faster, breathing quickened, and before long the kiss broke as Mabel let out a gasp, body tightening.

“Oh god, oh fuck Dipper I’m gonna-” she started, but the warning was cut off by the feeling of her borrowed length pulsating, ropes of sticky whiteness splattering out onto the floor of the attic. They’d clean it up later, for now all Mabel could think of was how amazing it was to feel that for the first time. Sure, lady orgasms were fun but that? That was a long slow buildup to one of the most intense and draining sensations ever. No wonder she heard that most guys could barely go more than once.

Dipper marveled at what had just transpired. He had never felt a dick other than his own when it came-or, well, that hadn’t changed, had it? But he’d felt it from another point of interest now. This was so overwhelming but too hot to worry about. “M-Mabes?” She opened her eyes and stared into his own dreamily. “I’m afraid I’m, er, having trouble deciphering the puzzle that is your ladyparts?” Sure, the fingers down there felt amazing, but all he seemed to be doing was stoking a fire to smolder slowly. A grin spread over his own face, and when he saw it do his sister’s eyebrow-thing he felt a tremor -was that out of fright or desire?-dance up her spine.

“Here, let big-bro take care of that for ya,” she teased, pushing him down on the bed and laying between her own legs. She shot him a wink, and before Dipper could ask what was happening he felt a tongue and a set of lips. Oh wow, oh WOW that was something else. Fingers had been one thing but THIS was in a league of it’s own! He tangled the fingers on his current set of hands down in his own hair, holding the controller of that tongue in place. He never wanted that feeling to end!

Mabel, meanwhile, wasn’t sure if her admiration for the new flavor she was experiencing was so enjoyable universally or because of her bro-bro’s taste buds. She didn’t care right at the moment, either, she’d decided. She was in the here and now. She licked and nibbled and kissed every sensitive spot she knew. The fact that it was her own vag she was going to town on made it a little easier. In her mind, this was some sort of weird form of masturbation. And hey, how many girls could say they had ate themselves out? Not many that weren’t contortionists, that was for certain!

Dipper couldn’t process thought very well, though. All he knew was he wanted more. He had a warm feeling building up in the middle of his torso. Yeah, the whole day up to this point, he had trouble thinking of the body he was in as his, but this sensation was something he wanted to own in the moment. When Mabel pushed a pair of his fingers into her own body, Dipper felt like somebody set off a charge.

The feeling of euphoria radiated out from hips to brain, coming in rippling waves of pleasure, one after the other. Holy cow, THIS was a female orgasm?! Guys got the short end of the deal with this stuff! He wanted-no, NEEDED-more, and he decided he was going to get it. Grip firm on his own hair, he clamped the thighs of his sister’s body around the head between them and rolled so that he was sat squarely on his own face. The strangeness of this was lost on him in the moment, all he cared about was getting another one of those orgasms.

Mabel tried to protest; the spin had yanked her borrowed fingers from her own body, so she used her hands to cling at the curvy hips that were swiveling, grinding against her, and tried to push her brother away. He only seemed to press down harder, rubbing more insistently. She mumbled something out, but the action only made Dipper twitch and writhe even more. When she guessed she wasn’t getting out without satisfying her… herself? Her brother? She wasn’t sure if her body was on autopilot or not. It did that sometimes when she was the one in it, so it stood to reason Dipper could lose control over it. The only way to calm it down was to give it a nice big 'gasm, so she set her bro-bro’s tongue to work.

Dipper couldn’t even mentally process what was happening. He seemed to be operating purely on instinct, his sister’s body leading the charge instead of his mind. Every little movement of the tongue against the flesh he had pressed to his own face would send another jolt through him. He felt another wave of pleasure mounting. When he rolled his sister’s sex just up against his own nose, it hit hard. Her body gave another buck of the hips, and that first wave was instantly followed by another, and then another. Girls got to have more than one orgasm at once?! This was super unfair!

While he writhed in bliss, Mabel writhed in desperation. Her brother was drowning her with her own juices. Or, well… drowning his own body with them. She gave her own backside a quick pinch to try and defuse the current situation, which apparently worked because Dipper yiped and jumped back, falling squarely on his own chest with her backside. Mabel greedily sucked in a breath of air, coughing to clear any congestion that had built up. “D-damn Dip, go easy on your shnozz! I know lady-gasms are nice but you’re gonna drown me. You. Whatever.”

He rolled off to the side, panting heavily, nodding in apology. “S-sorry. I never realized that girls got hit THAT hard when they came and could keep going. That’s intense!” Mabel chuckled, lifting a hand up to offer a high five. Her brother took the chance, their hands connecting noisily. He glanced down shortly after, laughing. “Well hey, looks like somebody got my refractory period to shorten,” he remarked, giving his sister’s growing arousal a poke. She squeaked and slapped his hand away.

“That’s hella sensitive, you ought to know that bro-bro!” He simply sniggered, shrugging. “Besides, as horned up as I am right now I, uh… I think it would be weird if this kept going.” Her body sat up and wiggled around to lean over top of her, and her brother’s eyes bore into her own, from her own face.

“How would it be any weirder than us both getting the other off?”

“Weeeelll… I dunno about you but I’m still a virgin. In there,” she stated flatly, poking her own body in the sternum. Dipper nodded.

“Yeah, me too. In fact I think you hit third base with my body before I did.” He sounded a little upset at that, and Mabel nodded back at him.

“My point 'zactly. If for any reason you, uh, would like to continue our sibling 'experiments’ in the pursuit of 'science’,” she stated, using finger-motions to highlight the words she was saying in quotation marks, “I would suggest we go hit that carpet downstairs in the basement again. So that we can at least each lose our virginity in our own bodies.”

“I… but… Mabel are you suggesting that we-?” Dipper started, but she planted a finger over the moving lips to shush him.

“Are you saying you don’t wanna?” After a couple of moments, she saw the debate behind those eyes end as her own head shook at her. “Then let’s get dressed and go make some sparks, static or otherwise!”

“Does this mean you yield and we can watch monster movies?” She frowned at her brother.

“Or we could just do science that night?”

Sharing a laugh, they each decided in that moment that whatever this was, they wanted to see where it went. Hand in hand, they ran down the stairs towards that dark room with an ugly old carpet lining the floor.


End file.
